Liquid level indicator systems

ABSTRACT

A liquid level indicator system for indicating the level of a conductive liquid in a reservoir includes a probe, at least a portion of the probe which is immersed in the liquid when the liquid level is at or above a predetermined level being coated with a layer of material which is absorbent to the conductive liquid so that a true indication of the liquid level in the reservoir is obtained.

United States Patent Parkes [4 1 Mar. 28, 1972 54] LIQUID LEVELINDICATOR SYSTEMS [56] References Cited [72] Inventor: Eric BernardParkes, Birmingham, En- I UNITED STATES PATENTS gland 1,862,244 6/1932Stuart.... ..204/283 [73] Assignee: Joseph Lucas (Industries) Limited,Bir- 1,433,017 10/1922 McKee ....204/290 mingham, England 2,944,9567/1960 Blue et al ..204/282 [22] Filed: 1969 Primary Examiner-John W.Caldwell [21] Appl. No.: 881,761 Assistant Examiner-H. Samuel CohenAttorney-Holman & Stern [30] Foreign Application Priority Data ABSTRACTDec. 20, 1968 Great Britain ..60,802/68 A liquid level indicator systemfor indicating the level of a 4 244C 204 280 quid a "Semi! includes a a6 2/l/00 portion of the probe which is immersed in the liquid when-the[58] i "264/282 340/244 liquid level is at or above a predeterminedlevel being coated with a layer of material which is absorbent to theconductive 7, liquid so that a true indication of the liquid level inthe reservoir is obtained.

,2 lei llpraw zefis r HWWUWW LIQUID LEVEL INDICATOR SYSTEMS Thisinvention relates to liquid level indicator systems, for indicating thelevel of conductive liquid in a reservoir, of the kind including aconductive probe, a conductive terminal, means for producing a potentialdifference between said probe and said terminal, and indicator means forindicating the absence of current flow between said probe and saidterminal, the arrangement being such that when the level of theconductive liquid is at or above a predetermined level the liquidbridges said probe and said terminalrand current flows between the probeand the terminal, whereas when the liquid level falls below saidpredetermined level said probe and said terminal are insulated from oneanother and no current flows, said indicator means then giving anindication that the liquid level is below said predetermined level.

in systems of the kind specified it is found that when the liquid levelis at or above said predetermined level, a layer of gas bubbles can formon the probe, thereby insulating the probe from said terminal andcausing a false indication of low liquid level to be given. It is anobject of the present invention to minimize this problem.

In a system of the kind specified, a portion of the probe which isimmersed in the liquid when the liquid level is at or above thepredetermined level is coated with a layer of material which isabsorbent to said conductive liquid.

The accompanying drawing is a diagrammatic representation of a vehicleradiator embodying a liquid level indicator system according to oneexample of the invention.

Referring to the drawing, the radiator 11 of the vehicle includes aheader tank 12 positioned above the radiator core 13. The header tank 12includes a neck 14 through which water can be inserted into theradiator, the neck 14 being closed by a cap 15, the desired water levelwithin the header tank 12 being indicated by a chain dotted line.Extending through the cap 15 into the header tank 12, but insulated fromthe walls of the tank 12 is a conductive probe 16 which terminates atits lower end, fractionally below the minimum desired water level. Theprobe 16 is electrically connected to a control unit 17 which derivesits power from the vehicle battery and which controls an indicator lamp18. A potential difference exists between the probe 16 and the wall ofthe header tank 12 and the control unit 17 is such that when theelectrical resistance between the probe 16 and the wall of the headertank 12 is at or above a predetermined level, then the lamp 18 isilluminated. In use, when the water level in the header tank 12 is at orabove the desired level then the water bridges the probe 16 and the wallof the header tank 12, reducing the resistance between the probe 16 andthe wall of the header tank 12 to below said predetermined value, sothat the lamp 18 is extinguished.

However, when the water level in the header tank 12 drops below thedesired level the probe 16 and the wall of the header tank 12 are nolonger bridged by the water, and so the resistance increases above thepredetermined value and the lamp 18 is illuminated to give an indicationof low water level in the radiator. I

It is found that in use, particularly when an ethylene glycolanti-freeze is added to the water in the radiator, a layer of gasbubbles tends to form around the immersed portion of the probe 16. Thelayer of bubbles on the immersed portion of the probe 16 tends toinsulate the probe 16 from the water and hence the wall of the headertank 12 thereby raising the electrical resistance between the probe 16and the wall of the header tank 12, and causing the lamp 18 to beilluminated, even though the water level within the radiator issatisfactory. Thus, a false indication of the water level in theradiator can be given.

In order to minimize the risk of such a false reading being given, dueto the formation of a layer of gas bubbles on the probe 16,- part or allof the immersed portion of the probe 16 has attached thereto a layer ofmaterial which absorbs water. For example, the end of the probe 16 canbe enclosed in a felt sleeve 21 which becomes impregnated with water,and it has been found that the provision of the absorbent layer on theend of the probe 16 is effective in inhibiting the formation of aninsulating layer of bubbles.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

l. A liquid level indicator system for indicating the level ofconductive liquid in a reservoir, the system including a conductiveprobe; a conductive terminal; said probe and said terminal beingarranged so that when the level of the conductive liquid is at or abovea predetermined level the liquid bridges said probe and said terminal,whereas when the liquid level falls below said predetermined level andsaid probe and said terminal are insulated from one another, and aportion of the probe which is immersed in the liquid when the liquidlevel is at or above the predetermined level being coated with a layerof material which is absorbent to said conductive liquid; a power sourcefor producing a potential difference between said probe and saidterminal so that when the level of the conductive liquid is at or abovethe predetermined level current flows between the probe and theterminal, but no current flows there between when the liquid falls belowsaid predetermined level; and indicator means for indicating the absenceof current flow between said probe and said terminal, said indicatormeans thereby giving an indication when the liquid level is below saidpredetermined level.

2. A system as claimed in claim 1 wherein the layer of absorbentmaterial is a felt sleeve.

1. A liquid level indicator system for indicating the level ofconductive liquid in a reservoir, the system including a conductiveprobe; a conductive terminal; said probe and said terminal beingarranged so that when the level of the conductive liquid is at or abovea predetermined level the liquid bridges said probe and said terminal,whereas when the liquid level falls below said predetermined level andsaid probe and said terminal are insulated from one another, and aportion of the probe which is immersed in the liquid when the liquidlevel is at or above the predetermined level being coated with a layerof material which is absorbent to said conductive liquid; a power sourcefor producing a potential difference between said probe and saidterminal so that when the level of the conductive liquid is at or abovethe predetermined level current flows between the probe and theterminal, but no current flows there between when the liquid falls belowsaid predetermined level; and indicator means for indicating the absenceof current flow between said probe and said terminal, said indicatormeans thereby giving an indication when the liquid level is below saidpredetermined level.
 2. A system as claimed in claim 1 wherein the layerof absorbent material is a felt sleeve.